Coaxial line terminating in cathode and control grid of cathode ray tube



March 19, 196s H. F. sci-MID 3,374,387 COAXIAL LINE TERMNATING IN CATHODE AND CONTROL GRID OF CATHODERAY TUBE Filed Nov. 18, 1966 BY W United States Patent Office 3,374,387 CGAXIAL LINE TERMINATING IN CATHODE CQNTROL GRID F CA'I'HODE RAY Hermann F. Schmid, San Francisco, Calif., assignor to the United States of America as represented by the Secretary of the Air Force Filed Nov. 18, i966, Ser. No. 595,537 2 Claims. (Cl. 315-3) ABSTRACT 0F THE DISCLOSURE An electron gun structure for use in a cathode-ray tube having a cathode, control grid, an additional modulating grid, and anode. The modulating grid and cathode form part of the outer and center conductor of a coaxial line. The coaxial line is brought out through the base of the cathode ray tube. The modulating signal is applied between the cathode and modulating grid.

This invention relates to an electron gun and more particularly to an electron gun structure for use in a cathode-ray tube which is capable of beam intensification with pulses of nanosecond duration.

A conventional gun for a cathode-ray tube usually consists of a cathode, control grid, and an anode and focusing system. The electrodes are connected by wires brought out through the base of the gun. The modulating voltage is applied between the cathode and the control grid.

The new gun of the present invention uses an additional grid, referred to as the modulating grid. This modulating grid and the cathode yform part of the outer and center conductor of a coaxial line, resulting in a structure of wide bandwidth, typically in the order of several gc. The coaxial line is brought out through the base. The modulating volta-ge is applied between the cathode and modulating grid.

Since the function of the conventional control grid is now performed by two grids, greater freedom in their design is obtained. It Ican be used to improve other characteristics, eg. to reduce the spot size or the driving Voltages required. It is also possible to use a fine wire mesh instead of the conventional aperture of the modulating grid. Instead of a coaxial structure, other -wide band structures c'an be used, eg., parallel plate or parallel wire lines.

An object of the invention is to provide a cathode-ray :gun to intensity modulate the beam.

Another object of the present invention is to provide a cathode-ray gun including an additional grid electrode used for modulating with the modulating grid and cathode forming part of the outer and center conductor of a coaxial line.

Various other objects, advantages, and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and objects obtained by its use, reference should be had to the subjoining drawings, which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated a preferred embodiment of the invention.

In the drawings:

FIGURE 1 illustrates the basic structure of a cathoderay tube which also includes a preferred embodiment of the gun structure of the present invention; and

FIGURE?, shows the modulating grid structure of the present invention.

Now referring in detail to FIGURE l, there is shown cathode-ray tube including beam 11 wherein deflection plates 12, anode and focusing structure 13, and view- Patented Mar. 19, 1968 ing screen 14 are conventional both in structure and operation. However, it is the gun structure in combination with the foregoing conventional structure which ycomprises the present invention. The gun structure is comprised of conventional control grid 15 having input pins 16 and 17, modulating grid 18, cathode 19, heater 20, wide band heater induct'ances 21, heater input pins 22 and 23, and coaxial line 24. Coaxial line 24 is comprised of outer conductor 25 and inner conductor 26. Modulating gnd 18 and cathode 19 form part of outer conductor 25 and inner conductor 26, respectively. Outer conductor 25 and inner conductor 26 also serve as inputs to modulating grid 18 and cathode 19, respectively.

Now referring to FIGURE 2 which is an enlarged detail view of the aforementioned gun structure, there is shown heater 20 with the associated wide band heater inductances 21 brought out through openings in coaxial line 24 to input heater pins 22 and 23. Control Igrid 15 is of conventional structure and is connected to input pins 16 and 17. yIt is to be noted that modulating grid 1S has been added to the standard control grid. In addition thereto, coaxial line 24 is part of the electron gun structure whose inner conductor 26 is the guns cathode, and whose outer conductor 25 terminates in a wire mesh modulating grid 18a interposed between the cathode emission surface 19a and control grid 15. Coaxial line 24 is brought out through the base of cathode-ray tube 10. The modulating voltage utilized to provide beam intensification is applied between the Icathode and modulating grid by Way of inner and outer conductors 25 and 26, respectively.

Since the function of the conventional control grid is now performed by two grids, greater freedom in their desi-gn is obtained. It can be utilized to improve other characteristics, c g., to reduce spot size or driving voltage. It is possible to use a fine wire mesh instead of conventional aperture of the modulating grid.

Instead of a coaxial structure, other wide band structure may be utilized, e.g., parallel plate or parallel wire lines.

Coaxial line 24 in the preferred embodiment was not terminated, thereby providing voltage doubling. The resultant reflections can be avoided by terminating the structure, if desired.

In the preferred embodiment, the gun structure is capable of producing `a display (dot) of a single pulse of 1 nsec. duration and 10 v. amplitude with the tube operated with an accelerating potential of 24 kv. The display can easily be observed with the naked eye. It should be possible to record pulses as short as several hundred picoseconds.

The spot size is approximately 0.004 inch for normal viewing brightness. The dynamic range of spot brightness Ifor typical applications is in the order of 20 db for single events and 30 db for repetitive events. The coaxial line 24 is 50 ohms and has a bandwidth of 3 gc. The cathode-ray tube also can be used for beam intensification with R.F. pulses of up to 3 gc. carrier frequency, in which case the structure acts as a detector. It is to be noted that beam intensification refers to the variation in spot brightness that is obtained when the beam current is varied by a modulating voltage.

In most applications the cathode-ray tube would use 'a roster scan, providing a simultaneous display of three lparameters on the X, Y, and Z-axes (brightness).

Numerous objects and advantages of the invention have been set forth in the foregoing description, together with details of the structure and the function of the invention, and the novel features thereof are pointed out in the appended claims. This disclosure however, is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts, within the principle of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

I claim as my invention:

1. In ya cathode-ray tube having a base, an electron gun structure consisting of a control grid having input pins thereto brought through said base, a coaxial line having an inner and outer conductor, said inner conductor terminating at one end in a cathode emissive surface, and said outer conductor terminating also at one end in a wire-mesh modulating glid with said Wire-mesh modulating grid interposed between said cathode emissive surface and said control Igrid, with the other ends of said inner and outer conductor being brought through said base of said cathode-ray tube to permit application thereacross of a modulation voltage, a heater associated with said cathode and disposed in said inner conductor adjacent to said cathode, wideband heater inductances connected to said heater, and heater input pins connected to said wideband heater inductances, said input heater pins also being brought through said base means for deiiecting electrons modulated -by said modulating grid,

and a display screen for visual observation of said modulation energy. v

2. In a cathode-ray tube having a base, an electron gun structure consisting of a control grid having input pins thereto brought through said base, a coaxial line having an inner and outer conductor, said inner conductor terminating at one end in a cathode emissive surface, and said outer conductor terminating also at one end in a single-aperture modulating grid with said single aperture modulating grid interposed between said cathode emissive surface and said control grid, with the other ends of said inner and outer conductor being brought through said base of said cathode-ray tube to permit application thereacross of a modulation voltage, a heater associated with said cathode and disposed in said inner conductor adjacent to said cathode, wideband heater inductances connected to said heater, and heater input pins connected to said wideband heater inductances, said input heater pins also being brought through said base means for deecting electrons modulated by said modulating grid, and a display screen for visual observation of said modulation energy.

References Cited UNITED STATES PATENTS 2,266,773* 12/1941 Law 313-82 X 2,399,223 4/1946 Haei 313-82 X 2,400,752 5/1946 Haeff 313-82 X 2,507,972 5/1950 Haei 313-82 X 2,720,611 10/1955 Sloan 313-82 X lROBERT SEGAL, Primary Examiner. 

